6o 
THE LIVING WORLD. 
posed that this was the only nidifying species, but more recent investigation 
discloses the fact that several fishes are peculiar in this respect in both fresh 
and salt water, as we shall see. 
The Sticklebacks are a small species belonging to the family Gastero- 
steidce , so called because of the sharp spines that project along the back. In 
some these spines are three in number, and again five, nine, or a dozen, each 
being a distinct species. In size they rank among the smallest of fishes, but 
are found in both fresh and salt water, and are common in Europe and 
America. The manner of constructing their nest, a service always performed 
by the male, is certainly curious. For this purpose the male is provided with 
an organ filled with a gelatinous secretion, which it voids through an opening 
in front of the vent, and 
NESTS OE THE STICKLEBACKS. 
which coagulates upon 
coming in contact with 
water, but which after 
voiding he carries about 
attached to his side. 
At the breeding sea¬ 
son, but before mating, 
the male selects a spot 
among aquatic plants, 
where a gentle current 
is continuous. He then 
begins his work by biting 
off small bits of plants 
and carrying them to the 
place of deposit, placing 
the first ones in an up¬ 
right position to serve as 
pillars. Other bits are 
now carried, each piece 
being glued fast by the 
substance which he se¬ 
cretes, until a layer is 
formed. His next step 
is to carry pebbles to the 
spot, with which he 
weights the layer and 
makes it substantial. Other layers, alternating with bits of plant and pebbles, 
are laid until the nest is made, arched over the top, leaving a cylindrical hole 
through the centre, which serves as the exit and entrance. The inner side 
is now well plastered with the glue from his body, and worked very smooth 
until it resembles varnish. Having completed his nest, he goes in search of 
a mate, to whom he makes love in an approved manner by a display of much 
vanity, involving a degree of activity which he manifests at no other time. 
When the female accepts his advances she immediately enters the nest and 
deposits her spawn, which usually occupies about five minutes. She then 
departs by the back door, when the male enters and ejects his milt over them 
in a much shorter time, then reappears and goes in search of another female, 
